Method of managing access to a random-access communication network

ABSTRACT

A device (D) is dedicated to communication management in a base station (SB) of a random access communication network. The device comprises processing means (MT) adapted i) to divide time intervals into time slots each associated with an access time slot during which a terminal (UE) is able to send an access request to the network and of width equal to the duration of an access request, ii) to divide said time intervals into sub-intervals (SI) including at least two consecutive time slots, iii) to designate in each sub-interval (SI) at least one prohibited time slot associated with a prohibited access time slot, iv) to define in each sub-interval (SI) a number, at least equal to the number of time slots that it contains, of windows (F) offset in time and of width equal to that of a time slot, and v), in the event of reception of an access request sent by a requesting terminal (UE), to deduce from the window (F) to which the access request belongs at least one access delay of the requesting terminal relative to a reference and then to determine from the access delay the time of sending an acknowledgement message to said requesting terminal (UE) so that it is able to receive it in a predefined acknowledgement time slot.

The invention relates to the field of random access communicationnetworks, and more particularly to managing communications within suchnetworks.

In certain networks of the type cited above, for example networksincluding slotted ALOHA access, communication terminals can transmittheir messages only during times authorized by the network.

To be more precise, when it first accesses the network, a requestingterminal must transmit to the base station signals representing apreamble defining a request for access with a view to transmitting amessage. To this end, it transmits the preamble with a signatureselected at random from N signatures (N=16 in the case of a UMTSnetwork, for example), in a specific random access channel (RACH), andin an access time slot of predefined width. In a slotted ALOHA typenetwork the preamble has a duration equal to 4096 chips, for example,and the width of a time slot is equal to 5120 chips (which correspondsto 1.3 ms).

Each terminal has a map of the access slots during which it isauthorized to send its preambles. This map, which is configurable, isbroadcast periodically over the whole of the coverage area of thenetwork, to all the terminals situated in that area. Moreover, the timereference of the base station is broadcast periodically by the networkover the whole of the coverage area to all of the terminals situated inthat area over a dedicated synchronization channel.

The requesting terminal can send the message associated with thetransmitted preamble only if said preamble has been acknowledged by thenetwork, more precisely by the base station. If the requesting terminalhas not received an acknowledgement message within a predefined andconfigurable acknowledgement time, it sends another preamble in anaccess slot. The number of preambles that can be sent consecutively andthe period with which the preambles are sent are predefined andconfigurable. They are broadcast periodically by the network over thewhole of the coverage area to all the terminals situated in that area.

A preamble is said to be acknowledged when the base station hasdetermined the presence of the terminal that sent it and the terminalhas received an acknowledgement message from the base station within theacknowledgement time cited above.

In the above type of network the time reference (or base) that isbroadcast, for example by a satellite, is received by the variousterminals present in the coverage area of that satellite, with a delayrelative to a reference that depends on their respective positions inthe area. Each terminal must lock its timebase onto the time referenceof the network. Now, because of the spread of the propagation timesbetween the satellite and the receiver modules of the terminals, thelatter are not synchronized with each other. The spacing between theauthorized access slots is therefore selected to define a guard time.

If the spread of propagation times is less than or equal to the guardtime, the preambles sent by the various terminals over different accesstime intervals are received by the base station within time slots thatcorrespond to the access time slots without risk of offsetting and/oroverlapping.

On the other hand, if the spread of the propagation times is greaterthan the guard time, the preambles sent by different terminals overdifferent access time slots are received by the base station offsetrelative to the receive windows associated with the access time slots.This can happen if the coverage area is enlarged, for example in thecase of “spot satellite” type coverage. The offset may be so great thatthe preambles may be received out of order. For example, in the case ofa European spot coverage, the spread of propagation times over roundtrip paths concerning satellites at an elevation from 20° to 40° canreach 13 ms, which corresponds to an offset of approximately ten accesstime slots. In the case of a national spot coverage, this spread canreach 4 ms, which corresponds to an offset of approximately three accesstime slots.

These offsets are liable to increase the risk of collision betweenpreambles, i.e. the probability that the base station receives more thanone preamble in the same access time slot. In the above example, this isreflected in a change from slotted ALOHA type access to ALOHA typeaccess, for the receive part, and consequently in a reduction of accesscapacity. Moreover, because of these offsets the receive time windows ofthe base station, which are locked to its time reference and of the samewidth as the access time slots, are no longer suitable.

To eliminate this problem, and more precisely to take account of thespread of propagation times, it has been proposed to define receive timewindows extending over a plurality of access time slots. This solutionhas a number of drawbacks, however. A plurality of preambles received inthe same receive time window might not be distinguished although they donot overlap (and therefore there is no collision). Moreover, because ofthe increased width of the receive time windows, the samples thatconstitute the signals defining the preambles received in a receive timewindow must be stored in a buffer for longer, which introduces anadditional processing delay. Finally, the calculation time is increased,with no possibility of parallel calculation.

An object of the invention is therefore to improve on this situation.

To this end it proposes a communication management method for a randomaccess communication network, consisting in:

-   dividing time intervals into time slots each associated with an    access time slot during which a terminal can send an access request    to the network, and of selected width greater than or equal to the    duration of an access request (or preamble) and then divide those    time intervals into sub-intervals including at least two consecutive    time slots and prohibit the terminals from sending access requests    during at least one of the access time slots associated with the    time slots of each sub-interval at the same time as authorizing them    to do so during non-prohibited access time slots,-   defining in each sub-interval a number, at least equal to the number    of time slots that it contains, of processing time windows offset in    time and of width substantially equal to that of a time slot, and-   deducing from the window to which a received access request belongs    at least one access delay of the requesting terminal relative to a    reference and then sending an acknowledgement message to that    requesting terminal at a moment selected as a function of that    access delay so that it can receive it in a predefined    acknowledgement time interval.

The method of the invention may have other features and in particular,separately or in combination:

-   the reception time of the message transmitted by a terminal    consecutively to the reception of an acknowledgement message sent in    response to an access request associated with said message may be    deduced from the access delay;-   the access delay may be stored in corresponding relationship to an    identifier of the requesting terminal so as to be able to time the    reception of each message sent by the terminal;-   the number of time slots of a sub-interval may be selected so that    it corresponds to the maximum spread of the access delays of the    terminals in a coverage area of the network. For example, the number    of time slots of a sub-interval may be equal to three and the use of    two consecutive time slots of three time slots in each sub-interval    may be prohibited;-   at least certain of the processing time windows may have a common    limit and/or certain of the processing time windows have a time    overlap, for example approximately equal to 50%;-   the time interval is equal to n times the duration of a radio frame    constituting the message associated with an access request, n being    greater than or equal to 1; for example, n is equal to 2;-   signals representing the access requests may be received in parallel    over each of the processing time windows of the sub-intervals so as    to deduce in parallel respective windows to which the received    signals belong from the access delays of the requesting terminals    relative to the reference, after which acknowledgement messages are    sent to the requesting terminals at times selected as a function of    their respective access delays, so that they are able to receive    them in the predefined acknowledgement time interval;-   signals representing the access requests may be received throughout    the duration of each sub-interval and an access delay may be    associated with each access request received during the sub-interval    as a function of the processing time window during which it was    received, after which acknowledgement messages may be sent to the    requesting terminals at times selected as a function of their    respective access delays so that they can receive them in the    predefined acknowledgement time interval.

The invention also proposes a communication management device for a basestation of a random access communication network, comprising processingmeans adapted to:

-   divide time intervals into time slots each associated with an access    time slot during which a terminal is able to send an access request    to the network and of selected width greater than or equal to the    duration of an access request,-   divide the time intervals into sub-intervals including at least two    consecutive time slots,-   designate in each sub-interval at least one time slot associated    with a prohibited access time slot during which the terminals are    prohibited from sending their access requests to the network,-   define in each sub-interval a number, at least equal to the number    of time slots that it contains, of processing time windows offset in    time and of width substantially equal to that of a time slot, and-   in the event of reception of an access request sent by a requesting    terminal, deduce from the window to which the access request belongs    at least one access delay of the requesting terminal relative to a    reference and then to determine from the access delay a time of    sending an acknowledgement message to the requesting terminal so    that it is able to receive it in a predefined acknowledgement time    slot.

The device of the invention may have other features and in particular,separately or in combination:

-   processing means adapted to determine from the access delay the time    of receiving the message sent by a terminal consecutively to the    receipt of an acknowledgement message sent in response to an access    request associated with the message;-   a memory adapted, on the instructions of the processing means, to    store each deduced access delay in corresponding relationship to an    identifier of the requesting terminal; in this case, the processing    means are adapted to instruct the receive timing of the base station    to be locked to each message sent by a terminal as a function of the    access delay associated with its identifier in the memory;-   a number of time slots of a sub-interval selected so that it    corresponds to the maximum spread of the access delays of the    terminals situated in a coverage area of the network;-   processing means adapted to define at least certain of the    processing time windows so that pairs of them have a common limit    and/or a time overlap, for example approximately equal to 50%;-   processing means adapted to receive signals representing the access    requests in parallel over each of the processing time windows of the    sub-intervals so as to deduce in parallel respective windows to    which the received signals belong from the access delays of the    requesting terminals relative to the reference, and then to command    the sending of acknowledgement messages to the requesting terminals    at delays selected as a function of their respective access delays,    so that they are able to receive them in the predefined    acknowledgement time interval;-   processing means adapted to receive signals representing the access    requests throughout the duration of each sub-interval and then to    associate an access delay with each access request received during    the sub-interval as a function of the processing time window during    which it was received, and then to command the sending of    acknowledgement messages to the requesting terminals at times    selected as a function of their respective access delays so that    they can receive them in the predefined acknowledgement time    interval.

The invention also relates to a base station (or gateway) for a randomaccess communication network equipped with a communication managementdevice of the type outlined above.

The invention is particularly well adapted, although not exclusively so,to managing calls of 3G type communication terminals, for example UMTStype 3G communication terminals operating in frequency division duplex(FDD) mode. Also, the invention is particularly well suited tocommunication networks including one or more communication satellites orrelay stations or radio repeaters, possibly of satellite type, connectedto a base station and causing much spreading of signal propagationtimes.

Other features and advantages of the invention will become apparent onreading the following detailed description and examining the appendeddrawings, in which:

FIG. 1 is a diagram of one embodiment of a portion of a satellitecommunication network including a base station equipped with a device ofthe invention,

FIG. 2 is a diagram of one example of the division of a time interval(IT) into time slots (T, TA and TI) and into sub-intervals (SI) of threetime slots, and

FIG. 3 is a diagram of one example of the definition of processing timewindows for the acquisition (or reception) in parallel of signalsdefining network access request preambles.

The appended drawings constitute part of the description of theinvention as well as contributing to the definition of the invention, ifnecessary.

An object of the invention is to enable adaptation of random access to acommunication network with one or more large coverage areas.

The following description considers, by way of illustrative example, asatellite type communication network with a slotted ALOHA type accessmechanism, as outlined in the introduction. However, the invention isnot limited to that type of network alone. It relates to allcommunication networks subject to a high spread (or divergence) ofsignal propagation times and which communication terminals can accessusing a random access procedure based on sending a preamble duringaccess time slots. Accordingly, the invention also relates tocommunication networks including relay stations or radio repeaters,possibly of satellite type, inducing high spreading of signalpropagation times.

In the present context, the expression “communication terminal” refersto any network equipment, and in particular any user equipment, such asa fixed or portable computer, a mobile telephone or a personal digitalassistant (PDA), or any server, capable of exchanging data in the formof signals either between themselves via the network to which they areconnected or with said network.

Moreover, it is considered hereinafter, by way of illustrative example,that the terminals are mobile telephone type user equipments (UE)connected to a 3G type communication network, such as a UMTS network,and operating in frequency division duplex (FDD) mode.

As shown in FIG. 1, a UMTS network with satellite access may, verybroadly speaking but nevertheless in sufficient detail for the inventionto be understood, be summarized as a core network (CN) coupled to anaccess network.

The satellite access network includes, firstly, at least one satellitebase station SB (or gateway) connected to the core network CN by anaccess node called the radio network controller (RNC) and integrating aNode B of the UMTS network and, secondly, at least one satellite SATadapted to exchange data by radio with the satellite base station SB andwith user equipments UE, such as mobile telephones, equipped with asatellite transceiver. The satellite link constitutes a satelliteinterface. Also, as the RNC has both service and control functions, itis called the controlling and serving RNC.

The Node B processes the signal in the base station SB. It is associatedwith one or more cells each covering a radio area containing one or moreuser equipments UE. The cell(s) of a Node B integrated into a satellitebase station SB are in the coverage area ZC of the satellite SATassociated with that satellite base station SB. Here the coverage areaZC is large, as in the case of what the person skilled in the art knowsas a spot satellite, for example.

In this type of satellite network, as indicated in the introduction,when a terminal UE wishes to communicate a message containing data, itmust, when it first accesses the network, send an access request (orpreamble) to the satellite base station SB, referred to hereinafter asthe gateway. To this end, the terminal UE generates a preambleaccompanied by a signature which, in the case of slotted ALOHA typeaccess, extends over a period of N chips, for example N=4096 chips. Inthe case of a UMTS network, the signature is chosen at random from 16signatures.

The terminal UE then transmits the preamble in the form of radio signalsto the satellite SAT covering the cell in which it is located, using adedicated random access channel (RACH) and in an authorized access timeslot. The satellite SAT then transmits the signed preamble to thegateway SB. The gateway SB must then execute a mechanism foracknowledging the received access request (or preamble) consistingfirstly in deducing from the time slot during which it receives thepreamble the access time slot used by the requesting terminal UE andthen deduce the access delay from the access time slot used.

In the present context, the expression “access delay” refers to the timeneeded for an access request (or preamble) generated by a terminal UE toreach the gateway SB via all the intermediate elements of the satelliteaccess network (Node B and SAT, and their respective connectioninterfaces).

The access delay varying as a function of the position of the requestingterminal UE in the coverage area ZC, a preamble sent by two distantterminals UE in the same access time slot T will be received by thegateway SB in different (offset) receive time intervals. Now, in anetwork with slotted ALOHA type access, each receive time intervalcorresponds to an access time slot, which corresponds to a fixed accessdelay. Consequently, in a large coverage area ZC, the preambles sent byterminals UE in the vicinity of its boundary may be received in receivetime intervals that do not correspond to the access time slot used,which may, on reception, generate preamble collisions that prevent theacknowledging of those preambles.

The invention is intended to remedy this drawback.

To this end it proposes a communication management device D installed inthe gateway SB and primarily comprising a processing module MT, as shownin FIG. 1.

The processing module MT is firstly responsible for dividing timeintervals IT into an integer number of time slots whose width is madeequal to the duration of an access time slot T. Hereinafter, the accesstime slots T used by the terminals UE to transmit their preambles (oraccess requests) are lumped together with the time slots resulting fromthe division of the intervals IT. Each time slot T therefore has a widthgreater than or equal to the duration of a preamble (or access request).Remember that the width of a time slot is equal to 5120 chips (whichcorresponds to 1.3 ms), while the width of a preamble is equal to 4096chips, for example.

As shown in FIG. 2, in the case of a UMTS network, each time interval IThas the maximum duration of a message, which is 20 ms. In fact, amessage may spread over one or two radio frames TR each of 10 msduration. Each time slot T of a time interval IT has a width of 1.3 ms,so a 20 ms time interval IT can therefore be divided into 15 time slots(T0 to T14).

Once this division has been effected, the processing module MT divideseach time interval IT into sub-intervals SI including at least twoconsecutive time slots T. In the FIG. 2 example, each sub-interval SIincludes three time slots T.

The processing module MT then designates in each sub-interval SI atleast one prohibited time slot TI corresponding to an access time slotduring which the terminals UE are prohibited from sending theirpreambles (or access requests) to the network. The time slots T whoseuse is not prohibited are called authorized time slots TA. Theycorrespond to the access time slots during which the terminals UE areauthorized to send their preambles to the network. In the FIG. 2example, each sub-interval SI includes a first authorized time slot TAfollowed by two prohibited time slots TI. However, other arrangementsmay be envisaged, of course.

The number of time slots T constituting a sub-interval SI, the number ofprohibited time slots TI and the number of authorized time slots TA ineach sub-interval SI are chosen to cover the maximum spread of delaysover the coverage area ZC concerned.

The information concerning the duration of the access time slots, themap of the access time slots, i.e. the authorized time slots TA and theprohibited time slots TI, the signatures, the minimum waiting timebetween two preamble sendings in the absence of reception of anacknowledgement message (or acknowledgement time interval), the delaybetween sending an acknowledged preamble and sending the associatedmessage, and the maximum number of preambles that may be sentconsecutively are broadcast periodically, in the conventional way, bythe gateway SB, via the access network, to the terminals UE situated inthe coverage area ZC of the satellite SAT.

Once this designation has been effected, the processing module MTdefines in each sub-interval SI a selected number of processing timewindows F having a width substantially equal to that of a time slot Tand offset in time. The number of processing time windows F persub-interval SI is at least equal to the number of time slots T thatsaid sub-interval SI contains. In the FIG. 2 multiwindowing example, sixprocessing windows (F1 to F6) are defined in each sub-interval SI. To bemore precise, in this example, three windows (F1 to F3) have a commonlimit and each extends over a time slot T, and three windows (F4 to F6)each extend over two halves of time slots T. The window F4 extends overthe time slots T0 and T1, the window F5 extends over the time slots T1and T2, and the window F6 extends over the time slots T2 and T3. Inother words, in this example, the window F4 has a 50% overlap with thewindows F1 and F2, the window F5 has a 50% overlap with the windows F2and F3, and the window F6 has a 50% overlap with the window F3 and withthe window F1 of the next sub-interval SI.

Of course, other processing time window F arrangements may be envisaged,with or without overlap.

The processing module MT therefore has a plurality of processing (orreception) windows offset in time but associated with an authorizedaccess time slot TA, so that it is able to receive in the variouswindows all of the preambles sent in the authorized access time slot TAregardless of their respective access delays. In the FIG. 2 example, thewindows F4 to F6 that overlap the windows F1 to F3 are intended toincrease the chances of detection, but above all to increase theaccuracy of detection.

When the processing module MT receives a preamble (or access request)sent by a requesting terminal UE, it is able to deduce from the windowin which it was received (or detected) the access delay of therequesting terminal UE relative to a time reference. That time referencecorresponds, for example, to the minimum network access delay of aterminal UE situated in the coverage area ZC concerned. For example, thefirst window F1 corresponds to the time reference and therefore to theminimum access delay, whereas the window F3 or F6 corresponds to themaximum access delay (i.e. that which exhibits the widest spread).

Once the processing module MT has deduced the access delay of apreamble, it is able to determine, from that access delay and from thepredefined waiting time between two preamble sendings (broadcastperiodically), the moment at which the gateway SB will have to transmitto the requesting terminal UE the message acknowledging the preamble forsaid terminal UE to receive it during the predefined waiting time.

That transmission time is of course defined relative to the timereference (or base) of the gateway SB.

Once the processing module MT has determined an acknowledgement messagetransmission time, it preferably determines, from the associated accessdelay, the time at which it will receive from the terminal UE themessage that it must transmit consecutively to receiving theacknowledgement message.

That reception time is defined relative to the time reference (or base)of the gateway SB, of course.

The processing module MT preferably stores each access delay previouslydeduced in a memory M of the device D in corresponding relationship tothe identifier of the corresponding requesting terminal UE.

That enables the processing module MT to instruct its gateway SB to lockits receiver onto each message that a given terminal UE is liable tosend subsequently, given the access delay that is associated with itsidentifier in the memory M.

The mechanism for determining the access delay(s) may be implemented inat least two different ways.

The first way is well suited to multiwindowing with overlap as shown inFIG. 2. Here, the processing module MT receives (or acquires) inparallel over each processing time window F defined in a sub-interval SIsignals representing access requests. It can therefore, in parallel,determine the access delays corresponding to the preambles received inthe various processing time windows F and instruct the gateway SB tosend acknowledgement messages to the requesting terminals UE at timescorresponding to their respective access delays. This reduces theprocessing times and increases the access capacity of the gateway SB(and therefore of the network).

The second way does not allow parallel processing. The processing moduleMT receives (or acquires) the signals representing preambles (or accessrequests) throughout the duration of a sub-interval SI, noting theirrespective arrival times. When the sub-interval has ended, it uses thedefinition of its processing time windows F to determine to which windowF each preamble received during said sub-interval SI belongs. It canthen associate an access delay with each preamble received during thesub-interval SI as a function of the processing time window during whichit was received. The processing module MT can then instruct the gatewaySB to send acknowledgement messages to requesting terminals UE at timescorresponding to their respective access delays in order for them to beable to receive them in the acknowledgement time interval previouslydefined.

In either event, there is restored at least the capacity to receive overall of the time slots associated with the authorized access time slotsTA, despite the large time spreads induced by the size of the coveragearea ZC. Thus the invention enables a W-CDMA type radio interface to beused as an IMT-2000 type satellite interface (in particular of the 3GPPUMTS type in FDD mode).

The management device D of the invention, and in particular itsprocessing module PM, and where applicable its memory M, may take theform of electronic circuits, software (or electronic data processing)modules, or a combination of circuits and software.

The invention also provides a communication management method for arandom access communication network.

This method may in particular be implemented with the aid of themanagement device D and the base station (or gateway) SB describedhereinabove. The main and optional functions and sub-functions of thesteps of the method being substantially identical to those of thevarious means constituting the management device D and/or the basestation (or gateway) SB, only the steps implementing the main functionsof the method of the invention are summarized hereinafter.

The method consists in:

dividing time intervals IT into time slots T each associated with anaccess time slot during which a terminal UE can send an access requestto the network, and of selected width greater than or equal to theduration of an access request (or preamble) and then divide those timeintervals IT into sub-intervals SI including at least two consecutivetime slots T and prohibit the terminals UE from sending access requestsduring at least one of the access time slots TI associated with the timeslots T of each sub-interval SI at the same time as authorizing them todo so during non-prohibited access time slots TA,

defining in each sub-interval SI a number, at least equal to the numberof time slots T that it contains, of processing time windows F offset intime and of width substantially equal to that of a time slot T, and

deducing from the window F to which a received access request belongs atleast one access delay of the requesting terminal UE relative to areference and then sending an acknowledgement message to that requestingterminal UE at a moment selected as a function of that access delay sothat it can receive it in a predefined acknowledgement time interval.

The invention is not limited to the management device, base station andmanagement method embodiments described hereinabove by way of exampleonly, and encompasses all variants that the person skilled in the artmight envisage that fall within the scope of the following claims.

Thus the foregoing description refers to a random access satellitecommunication network equipped with one or more satellite base stations(or gateways). The invention is not limited solely to this type ofrandom access network, however. It relates to all random accesscommunication networks in which there is a large spread (or divergence)of signal propagation times between a base station (or gateway) andcommunication terminals, and in particular communication networksincluding relay stations or radio repeaters, possibly of the satellitetype, connected to a base station.

1. Communication management method for a random access communicationnetwork, characterized in that it comprises: dividing time intervals(IT) into time slots (T) each associated with an access time slot duringwhich a terminal (UE) can send an access request to the network, and ofselected width greater than or equal to the duration of an accessrequest and then divide those time intervals (IT) into sub-intervals(SI) including at least two consecutive time slots and prohibit theterminals from sending access requests during at least one of the accesstime slots associated with the time slots (T) of each sub-interval atthe same time as authorizing them to do so during non-prohibited accesstime slots, defining in each sub-interval (SI) a number, at least equalto the number of time slots (T) that it contains, of processing timewindows (F) offset in time and of width substantially equal to that of atime slot (T), and deducing from the window (F) to which a receivedaccess request belongs at least one access delay of the requestingterminal (UE) relative to a reference and then sending anacknowledgement message to that requesting terminal (UE) at a momentselected as a function of that access delay so that it can receive it ina predefined acknowledgement time interval.
 2. Method according to claim1, characterized in that a reception time of a message transmitted by aterminal (UE) consecutively to the reception of an acknowledgementmessage sent in response to an access request associated with saidmessage is deduced from said access delay.
 3. Method according to claim1, characterized in that said access delay is stored in correspondingrelationship to an identifier of the requesting terminal (UE) so as tobe able to time the reception of each message sent by said terminal(UE).
 4. Method according to claim 1, characterized in that said numberof time slots (T) of a sub-interval (SI) is selected so that itcorresponds to the maximum spread of the access delays of the terminals(UE) in a coverage area (ZC) of said network.
 5. Method according toclaim 1, characterized in that said number of time slots (T) of asub-interval (SI) is equal to three.
 6. Method according to claim 5,characterized in that the use of two consecutive time slots (TI) ofthree time slots in each sub-interval (SI) is prohibited.
 7. Methodaccording to claim 1, characterized in that at least certain of saidprocessing time windows (F) have a common limit.
 8. Method according toclaim 1, characterized in that certain of said processing time windows(F) have a time overlap.
 9. Method according to claim 8, characterizedin that said time overlap is substantially equal to 50%.
 10. Methodaccording to claim 1, characterized in that said time interval (IT) isequal to n times the duration of a radio frame constituting said messageassociated with an access request, n being greater than or equal to 1.11. Method according to claim 1, characterized in that signalsrepresenting said access requests are received in parallel over each ofthe processing time windows (F) of the sub-intervals (SI) so as todeduce in parallel respective windows (F) to which said received signalsbelong from the access delays of the requesting terminals (UE) relativeto said reference, after which acknowledgement messages are sent to saidrequesting terminals (UE) at times selected as a function of theirrespective access delays, so that they are able to receive them in saidpredefined acknowledgement time interval.
 12. Method according to claim1, characterized in that signals representing said access requests arereceived throughout the duration of each sub-interval (SI) and an accessdelay is associated with each access request received during saidsub-interval (SI) as a function of the processing time window (F) duringwhich it was received, after which acknowledgement messages are sent tosaid requesting terminals (UE) at times selected as a function of theirrespective access times so that they can receive them in said predefined acknowledgement time interval.
 13. Communication managementdevice (D) for a base station (SB) of a random access communicationnetwork, characterized in that it comprises processing means (MT)adapted to: divide time intervals into time slots (T) each associatedwith an access time slot during which a terminal (UE) is able to send anaccess request to the network and of selected width greater than orequal to the duration of an access request, divide said time intervals(IT) into sub-intervals (SI) including at least two consecutive timeslots (T), designate in each sub-interval (SI) at least one prohibitedtime slot (TI) associated with an access time slot during which theterminals (UE) are prohibited from sending their access requests to thenetwork, define in each sub-interval (SI) a number, at least equal tothe number of time slots (T) that it contains, of processing timewindows (F) offset in time and of width substantially equal to that of atime slot (T), and in the event of reception of an access request sentby a requesting terminal (UE), deduce from the window (F) to which saidaccess request belongs at least one access delay of the requestingterminal (UE) relative to a reference and then to determine from saidaccess delay a time of sending an acknowledgement message to saidrequesting terminal (UE) so that it is able to receive it in apredefined acknowledgement time slot.
 14. Device according to claim 13,characterized in that said processing means (MT) are adapted todetermine from said access delay a time of receiving a message sent by aterminal (UE) consecutively to the receipt of an acknowledgement messagesent in response to an access request associated with said message. 15.Device according to claim 13, characterized in that it comprises amemory (M) adapted, on the instructions of said processing means (MT),to store each deduced access delay in corresponding relationship to anidentifier of the requesting terminal (UE) and said processing means(MT) are adapted to instruct the receive timing of said base station(SB) to be locked to each message sent by a terminal (UE) as a functionof the access delay associated with its identifier in said memory (M).16. Device according claim 13, characterized in that said number of timeslots (T) of a sub-interval (SI) is selected so that it corresponds tothe maximum spread of the access delays of the terminals (UE) situatedin a coverage area (ZC) of said network.
 17. Device according to claim13, characterized in that said number of time slots (T) of asub-interval (SI) is equal to three.
 18. Device according to claim 17,characterized in that said processing means (MT) are adapted todesignate on command two consecutive prohibited access time slots (TI)of three time slots in each sub-interval (SI).
 19. Device according toclaim 13, characterized in that said processing means (MT) are adaptedto define at least certain of said processing time windows (F) so thatpairs of them have a common limit.
 20. Device according to claim 13,characterized in that said processing means (MT) are adapted to defineat least certain of said processing time windows (F) so that they have atime overlap.
 21. Device according to claim 20, characterized in thatsaid time overlap is substantially equal to 50%.
 22. Device according toclaim 13, characterized in that said time interval (IT) is equal to ntimes the duration of a radio frame constituting said message associatedwith an access request, n being greater than or equal to one.
 23. Deviceaccording to claim 13, characterized in that said processing means (MT)are adapted to receive signals representing said access requests inparallel over each of the processing time windows (F) of thesub-intervals (SI) so as to deduce in parallel respective windows (F) towhich said received signals belong from the access delays of therequesting terminals (UE) relative to said reference, and then tocommand the sending of acknowledgement messages to said requestingterminals (UE) at times selected as a function of their respectiveaccess delays, so that they are able to receive them in said predefinedacknowledgement time interval.
 24. Device according to claim 13,characterized in that said processing means (MT) are adapted to receivesignals representing said access requests throughout the duration ofeach sub-interval (SI) and then to associate an access delay with eachaccess request received during said sub-interval (SI) as a function ofthe processing time window (F) during which it was received, and then tocommand the sending of acknowledgement messages to said requestingterminals (UE) at times selected as a function of their respectiveaccess delays so that they can receive them in said predefinedacknowledgement time interval.
 25. Base station (SB) for a random accesscommunication network, characterized in that it comprises at least onecommunication management device (D) according to claim
 13. 26. Use ofthe communication management method according to claim 1 for 3G typecommunication terminal communication management.
 27. Use according toclaim 26, characterized in that said 3G communication terminals are UMTSnetworks operating in frequency duplex mode.
 28. Use according to eitherclaim 26, characterized in that said communications take place insatellite type random access communication networks.
 29. Use accordingto claim 26, characterized in that said communications take place inrandom access communication networks with radio relay stations coupledto a base station.
 30. Use of the communication management device (D)according to claim 13 for 3G type communication terminal communicationmanagement.
 31. Use of the base station (SB) according to 3G typecommunication terminal communication management.